International Journal of Comparative Psychology

Rats in a vehicle treated control condition when shifted from 4% to 32% sucrose displayed successive positive contrast by responding at a significantly higher lick rate in a 5 min trial than rats maintained on 32% sucrose throughout the experiment. In contrast, rats treated with an escalating dose regimen of D-amphetamine (1-10 mg/kg) over a 4 day interval failed to display successive positive contrast. Withdrawal from drug treatment had no effect on lick rate or response latency in rats maintained on 32% sucrose. These data are consistent with many previous reports that withdrawal from a binge-like regimen of psychostimulant drug administration disrupts responding for natural reward stimuli. These findings support the use of psychostimulant withdrawal as a model of drug-induced dysphoria and suggest that incentive contrast is a particularly sensitive measure of these changes in motivation and emotion.